Making Prehistory

Researchers digitize a cave-art gallery

By Jenny Donelan

Not so many years ago, if you wanted to see prehistoric cave art in its original setting, you could. You might visit Altamira in Spain or Lascaux in France, where, standing in the caves of our Paleolithic ancestors, you could view the stylized and vibrant bison, horses, and other beasts they painted there some 15,000 years ago. Sadly this close-up experience is now available to few people, because by visiting the cave paintings, humans had begun to destroy them. The carbon dioxide that visitors exhaled was making the atmosphere inside the caves more acidic, dissolving the surfaces of the limestone walls and loosening the paintings. At the same time, all those tourists-as many as 1000 a day at Altamira in the 1970s-were raising temperatures inside the caves to the point where bacteria began growing on the artwork.

In order to protect the ancient illustrations, most European countries stopped widescale access to cave galleries about 25 years ago. But because the caves represented sources of national pride and in come, the idea of creating life-size replicas wasn't long to follow. A notable effort in the 1980s was Lascaux II in France, for which two of the cave's galleries were reproduced using manual measurements and photogrammetry. In Spain, various government and research bodies began toying with a similar idea-a particularly ambitious reproduction of Altamira, where the paintings are notable for their beauty, use of multiple colors, and incorporation of natural rock features that create a kind of bas-relief effect.

In 1988, Spanish agencies selected the Madrid-based replication specialists at Tragacanto to create a facsimile of Alta mira that was true to the original not only in spirit, but in as many particulars as possible. Explains Sven Nebel, technical director for Tragacanto, "Replication is necessary for all painted caves visited on a massive scale. But it must be done carefully, not in a 'Disney' way."

Tragacanto was able to begin the project with data provided by the National Geo graphic Institute of Spain, which had earlier spent eight months making point laser measurements along every 5mm of the main chamber. Tragacanto then used a Minolta VI-700 3D Digitizer to scan additional, more complicated parts of the cave at even higher resolutions. Tragacanto's Manolo Franquelo oversaw the coordination of both datasets using numerous hardware and software products-a list that includes Golden Software's Surfer7, Inus Technology's Rapidform 2000, Auto desk's AutoCAD, and many others-for the project. The team then used the combined data to mill a set of 1/10 scale models of different parts of the cave.

The Paleolithic artists who painted these bison in the cave at Altamira in northern Spain used both a variety of pigments and the natural features of the rock ceiling to create complex representations that are considered among the finest in prehistoric ar

Based on suggestions from scientists and other researchers, Tragacanto made sizing tweaks and other changes to the physical models, digitized them, fed the data back into a digital model, then recreated the 1/10 physical models, repeating the process several times before everyone involved with the project was satisfied. Then, to make the 200-square-meter ceiling section of the cave (where most of the paintings appear) on a 1:1 scale, the data was fed into a larger milling machine that created pieces of the cave from large blocks of medium-density polystyrene foam. Afterward, a wax skin with details not captured in the original scanning process-hairline scratches, small bubbles, etc.-was applied to the foam blocks.

Tragacanto used RapidForm 2000 and software from Minolta to bring each scan into a common 3D coordinate system for making a model of the cave. The section above represents more than a year's worth of work.(Image courtesy Minolta.)

For the sides and floor of the cave, an area of approximately 2400 square meters, scan data was used to position the cave on the building planes prescribed by architects at the replica's future home, The Museum and Research Centre of Altamira (located within walking distance of the original cave). The finished model was sliced into sections approximately 30 meters long, and the final synthetic rock replica was made from that. This rock material consists of 80 percent powdered limestone with an absorbency similar to that of the real cave, and 20 percent binders. Then professors Pedro Saura and Matilde Muzquiz of the Complu tense University of Madrid handpainted the ceiling bestiary onto the rock replica, using the same kinds of mineral pigments and charcoal that researchers believe the Altamira artists used.

The 13-year project was finished in 2001. Now, as many as 2000 visitors a day enter the exactingly created replica, which is regulated to 18 degrees Celsius, like its real counterpart. Although this museum experience cannot possibly be as exciting as clambering into a real cave and viewing actual 15,000-year-old paintings, the replica provides visitors with at least a taste of the atmosphere in which Paleolithic artists created their haunting masterpieces.

Key Tool: Minolta VI-700 3D Digitizer, Minolta (www.minolta-3d.com)

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